Let me first say am far from any kind of expert but i have had many differnt brands from generic to namebrands like scandisk. Some are a little faster in writing to the card than others but i find its not tha big a deal. But if i was shooting with a 6 mega pixel camera as opposed to my 3.3 i mite change my mind. I have heard some say that certain brands of cards dont work in some cameras but my experience is even the cheapest generic cards worked in the differnt cameras i have had. Like I said i think speed in writing to the card is the only differnce and if your not some professional i stick with whatever i can get cheaper.

Some brands won't have full compatibility. I've got a 256mb Mr. Flash card that won't work in my Dimage 7 but works like a champ in a Canon A10. I also got some 128mb BSA media cards that were inexpensive but noticably faster than 4x Lexar cards.

on some pro cameras there is a difference and as padeye said- some no name no work with all brands. the controllers in the cards themselves are what make the difference. sandisk uses a sandisk controller. delkin- a toshiba controller. lexar- a lexar designed controller. go to this link and you can get a good idea on the differences. http://www.robgalbraith.com/media/co...ash/index.html
mr. galbraith references the timings and transfer rates to popular pro cameras. the xfer rate will vary from your camera and mine. due to their interface controller. each camera will have its own quirks and issues. i look at the warrentee in case they decide to die on me. sandisk ultra and delkin are i believe are lifetime. lexar is i think 5 years. i have used these 3 brands and i feel i can count on them. when your looking at a $320 512MB life time warrentee card from a brand you know vs $290 "who made it?" card you gotta ask your self- Do you feel lucky?
if they offer a lifetime warrentee who is going to back it up if you can't find them after a year or two. the brands i mentioned are fairly solid in the photo community. thats not to say in the current economic eviornment things happen